1. Field of the Invention
This invention relates generally to a safety control device for actuators of the flap solenoid valve type and more particularly to a safety control device for actuators of a flap solenoid valve used in automatic transmissions.
2. Discussion of the Background
For several years, electronic control systems have been used for the injection of gas or diesel fuel, for automatic transmissions, for the brake elements, for steering elements, and for suspension elements using, electrohydraulic actuators, flap solenoid valves of the fuel injector type or of the pressure modulator type, for example. Very generally, these actuators are of the solenoid type and exhibit the feature of having a hydraulic channel which can be opened or closed very quickly a very large number of times without functional degradation for the service life of the product. The electromagnetic force developed by the solenoid in the magnetic circuit of the actuator allows the closing or opening of the hydraulic channel by moving a mobile unit which can consist either directly of a solenoid plunger, a ball, a plate, etc. which is in the magnetic flux, or indirectly of a hydraulic slide magnetically insulated from the actuator but actuated by a solenoid plunger, a ball, a plate, etc. which is in the magnetic flux. When the solenoid is not supplied with power, the force exerted by the pressure of the fluid itself and/or by the action of a spring inversely causes the opening or closing of the hydraulic channel.
Very generally, the resistance of the solenoid is selected to be as low as possible in order to reduce as much as possible the time of movement of the mobile unit which disturbs the functional response of the actuator. This arrangement increases the rise and fall of the current in the solenoid upon the appearance of the activation or deactivation order to cause the electromagnetic force to rise or fall more quickly.
In order to reduce the energy dissipated by the actuator when the mobile unit is held at the end of its travel and when the current which passes through the solenoid reaches a so-called "call" value, the current is reduced and maintained only by a limitation electronic device at a so-called "maintaining" value.
It is clear that any electric anomaly, such as shortcircuit, open circuit, abnormal resistance which affects the operation of such an actuator, can have very harmful consequences on the good operation of the element controlled, on its mechanical strength and even on the safety of the occupants of the vehicle. Known monitoring and cutoff devices associated with flap solenoid valves described above are ineffective to solve this problem. Actually, these device are generally designed so that the monitoring of the electrical operation of the solenoid valve is done by a measurement of the intensity of the current passing through the solenoid and/or the voltage present either directly at its terminals, or at the terminals of the controlling electric switching element placed in series with the solenoid valve and by comparative and synchronous analysis of the values measured in relation to known patterns representing the various combinations possible during good or poor operations of the device. In the case of flap solenoid valves, the values of the intensity of the current passing through the solenoid and the voltage at its terminals or at the terminals of the switching element are essentially variable over time, particularly because of the action of the limitation system of the current and, consequently, cannot be compared simply with patterns established in advance. This makes such a method of diagnostics of an operational anomaly ineffective. The principle of insulation of the solenoid valve with respect to its electric connections generally is used by the cutting off of the circuit downstream from the solenoid valve by direct action on the switching element itself or, even better, by additional cutting off of the circuit upstream from the solenoid valve by action on an appropriate conductive/nonconductive device, so as to achieve a complete galvanic insulation of the 2 outlets of the solenoid valve to which it is desired to cut off the power supply.